The present invention relates to an analyzer circuit for an inductive sensor, particularly for a an inductive position sensor for the position of a moving part based on the eddy current principle.
To determine the position of a part, especially an adjusting element of a control device, an inductive position transmitter has been used, in which a change in the inductance of at least one, advantageously two, coils, depends on the position of the part. The inductance value is then a measure of the position of the part. Usually the analyzer circuit of this type of detector is provided with an oscillator means and an oscillator circuit branch. U.S. Pat. No. 4,644,570 describes an example of this type of inductive position sensor and/or an associated analysis circuit. In this apparatus the position detecting means is a differential sensor, which means, that both inductances change oppositely to each other with the varying position of the moving part. Both coils, which cooperate with a core according to the eddy current principle, are alternately connected to a condenser according to whether it is closer to the one coil or the other, so that in the one position a first circuit branch is connected and in the other position a second circuit branch is connected. Both oscillator circuit branches are driven successively with an oscillator of an oscillator circuit in which the associated eigenfrequencies change according to position because of the position-dependent inductance values. The evaluation of these eigenfrequencies allows a determination of the position of the part.
A disadvantage of the known inductive sensor and/or the associated analysis circuit is that it has a comparatively low sensitivity and furthermore is nonlinear in its response. Furthermore oscillations can occur because of the switching of the oscillator circuit branches, which can lead to erroneous results for the position measurement. An additional advantage is that the output signal is analog or pulse width modulated so that an analog-to-digital converter is required prior to a digital analysis process.